Ali was the first man to win the heavyweight title of the world three times and won the BBC's Sports Personality of the Century award in 1999.

Apart from his achievements in the ring Ali has also come to be seen as one of the iconic figures of the 20th century for the way he lived his life away from boxing.

He refused to fight in the Vietnam War, was stripped of his world title and banned from boxing.

He was allowed to fight again in 1970 after three years out of the ring and finally regained his title in 1974 when he beat George Foreman in the "Rumble in the Jungle", probably the most talked-about fight in history.

A powerful activist for black rights, both in America and around the world, he changed his name from Cassius Clay to Muhammad Ali in 1964 after joining the Nation of Islam.

"He's done a remarkable job for boxing, for himself and even for minorities," said Lewis.

"He's definitely a great man."

In later years Ali has been affected by Parkinson's disease, which has been attributed to repeated blows to the head during his boxing career.

Lewis saw Ali recently when he attended an event where Ali was watching his daughter Laila fight.

"He looked as well as he could look," said Lewis.

"Parkinson's is a disease that comes and goes - some days it's better than others.

"On the day I saw him I think he was a bit shaky but I know there are other days that he's not."

Former British and Commonwealth heavyweight champion Henry Cooper twice fought Ali, famously flooring him in their first encounter, when Ali was only just saved by the bell.

"When you're young you are rivals, and now it's a shame to see him that way (suffering with Parkinson's Disease).

"Whenever we meet he always gives me a big bear hug and we talk, we're friendly and that's how it should be.

"We are friends. For my 50th birthday he came over and helped me celebrate and he's a great character."